Wednesday, February 27, 2013

This Day in History: Feb 27, 1964: Leaning Tower needs help

On February 27, 1964, the Italian government
announces that it is accepting suggestions on how to save the renowned
Leaning Tower of Pisa from collapse. The top of the 180-foot tower was
hanging 17 feet south of the base, and studies showed that the tilt was
increasing by a fraction every year. Experts warned that the medieval
building--one of Italy's top tourist attractions--was in serious danger
of toppling in an earthquake or storm. Proposals to save the Leaning
Tower arrived in Pisa from all over the world, but it was not until 1999
that successful restorative work began.

On August 9, 1173,
construction began on the Leaning Tower, which was to house the bells of
the vast cathedral of the Piazza dei Miracoli, the "Place of Miracles."
Pisa at the time was a major trading power and one of the richest
cities in the world, and the bell tower was to be the most magnificent
Europe had ever seen. However, when the tower was just over three
stories tall, construction stopped for an unknown reason. It may have
been because of economic or political strife, or the engineers may have
noticed that even then, the tower had begun to sink down into the ground
on one side.

In recent years, it has been determined that the
tower's lean is caused by the remains of an ancient river estuary
located under the building. The ground is made up in large part of water
and silty sand, and one side of the heavy marble building began
gradually sinking into the ground as soon as the foundation was laid.
The
95-year pause in construction allowed the building to settle somewhat,
and the new chief engineer sought to compensate for the tower's visible
lean by making the new stories slightly taller on the short side. In
1278, workers reached the top of the seventh story, and construction was
halted again. By that time, the southward tilt was nearly three feet.

In
1360, work began on the bell chamber, the eighth and final story, and
workers attempted to compensate for the lean by building the chamber at a
slight slant with the rest of the tower. The tower was officially
completed about 1370. Despite its growing lean, the building was
acclaimed as an architectural wonder, and people came from far and wide
to admire its 200 columns and six external arcades.

The lean grew a
little every year, but this only increased interest in the tower. A
measuring from 1550 showed the top was 12 feet south of the base. In
1838, an architect was given permission to excavate the base of the
tower, a portion of which had sunk into the ground. As he dug, water
came sprouting out of the ground, and the tower tilted another few
inches south.

In 1934, Benito Mussolini,
the dictator of Italy, decided that the Leaning Tower was an
inappropriate symbol for masculine Fascist Italy. In an attempt to
reverse the tilt, engineers drilled holes into the foundation of the
tower, and some 200 tons of concrete was poured in. The tower abruptly
lurched another few inches south.

In the 1950s,
the heavy medieval bells in the tower were locked tight. In 1964, the
Italian government publicly asked for suggestions on how to save the
tower from what they believed was a forthcoming collapse. Two years
later, a restorative attempt involving drilling was aborted when the
tower tilted another fraction south. In 1985, another boring attempt
likewise caused an increase in the lean. In 1990, the Italian government
closed the Leaning Tower's doors to the public out of safety concerns
and began considering more drastic proposals to save the tower.

In
1992, in an effort to temporarily stabilize the building,
plastic-coated steel tendons were built around the tower up to the
second story. The next year, a concrete foundation was built around the
tower in which counterweights were placed on the north side. The use of
these weights lessened the tilt by nearly an inch. In 1995, the
commission overseeing the restoration sought to replace the unsightly
counterweights with underground cables. Engineers froze the ground with
liquid nitrogen in preparation, but this actually caused a dramatic
increase in the lean and the project was called off.

Finally, in
1999, engineers began a process of soil extraction under the north side
that within a few months was showing positive effects. The soil was
removed at a very slow pace, no more than a gallon or two a day, and a
massive cable harness held the tower in the event of a sudden
destabilization. Within six months, the tilt had been reduced by over an
inch, and by the end of 2000, nearly a foot. The tower was reopened to
the public in December 2001, after a foot-and-a-half reduction had been
achieved. It is thought that those 18 inches will give another 300 years
of life to the Leaning Tower of Pisa.

Timeline

On January 5, 1172, Donna Berta di Bernardo, a widow and resident of the house of dell'Opera di Santa Maria, bequeathed sixty soldi to the Opera Campanilis petrarum Sancte Marie. The sum was then used toward the purchase of a few stones which still form the base of the bell tower.[9]

On August 9, 1173, the foundations of the Tower were laid.

Nearly four centuries later Giorgio Vasari
wrote : "Guglielmo, according to what is being said, in [this] year
1174 with Bonanno as sculptor, laid the foundations of the bell tower of
the cathedral in Pisa."

Another possible builder is Gerardo di Gerardo. His name appears as a
witness to the above legacy of Berta di Bernardo as "Master Gerardo",
and as a worker whose name was Gerardo.

A more probable builder is Diotisalvi,
because of the construction period and the structure's affinities with
other buildings in Pisa. But he usually signed his works, and there is
no signature by him in the bell tower.

Giovanni di Simone was heavily involved in the completion of the tower, under the direction of Giovanni Pisano,
who at the time was master builder of the Opera di Santa Maria
Maggiore. He could be the same Giovanni Pisano who completed the belfry
tower.

Giorgio Vasari indicates that Tommaso di Andrea Pisano was the designer of the belfry between 1360 and 1370.

On December 27, 1233, the worker Benenato, son of Gerardo Bottici,
oversaw the continuation of the construction of the bell tower.[10]

On February 23, 1260, Guido Speziale, son of Giovanni, a worker on
the cathedral Santa Maria Maggiore, was elected to oversee the building
of the Tower.[11]

On April 12, 1264, the master builder Giovanni di Simone and 23
workers went to the mountains close to Pisa to cut marble. The cut
stones were given to Rainaldo Speziale, worker of St. Francesco.[12]